20=-16t2+64t+4

Solution for 20=-16t2+64t+4 equation:

20=-16t^2+64t+4

We move all terms to the left:

20-(-16t^2+64t+4)=0

We get rid of parentheses

16t^2-64t-4+20=0

We add all the numbers together, and all the variables

16t^2-64t+16=0

a = 16; b = -64; c = +16;
Δ = b2-4ac
Δ = -642-4·16·16
Δ = 3072
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$t_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{3072}=\sqrt{1024*3}=\sqrt{1024}*\sqrt{3}=32\sqrt{3}$
$t_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-64)-32\sqrt{3}}{2*16}=\frac{64-32\sqrt{3}}{32}
$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-64)+32\sqrt{3}}{2*16}=\frac{64+32\sqrt{3}}{32}
$